A motorcycle comes into the shop with complaints of a dragging or slipping clutch. Before jumping in and replacing the clutch plates, quickly check the clutch cable free play and any other clutch adjustment features on the particular model. Many new or nontechnical riders end up riding around with clutches far out of adjustment. Not only can this make for a poor performing clutch, but it can accelerate the wear of the clutch components.
If all of the adjustments are within specification, and the clutch is still failing to behave correctly, the clutch components need to be inspected. In most cases the bike will require a new set of clutch friction plates, but there are other components that should be inspected while working with the clutch.
Measure the length of the clutch springs to check for fatigue. Replace all of the clutch springs as a set if one is out of the service limit or the lengths vary dramatically across the set.
A typical motorcycle wet clutch pack consists of around 6 steel discs and the same number plus one frictions discs. However, special clutch plates and/or judder springs may also be included. These special plates may have a different inside diameter to fit over a judder spring and seat, or a different friction material, different tangs, or special markings. Pay attention as the clutch pack is disassembled. Note the placement and orientation of any special clutch plates or judder springs.
Look for signs of damage on the clutch plates. Check the steel plates for warp and discoloration. The service manual will have specifications for inspecting the clutch plates, but usually there is plain evidence of the need for new clutch plates.
Check the clutch basket and hub for wear and damage. If the basket or hub become overly pitted the pack will not be able to expand and contract smoothly. Also, check the condition of the clutch lifter/pusher components and bearings.
Be sure to soak the new friction plates in oil prior to installation. Do the same with the steel plates if they are dry or new. A wet clutch is sensitive to the type of oil used, so use the correct motorcycle oil for the application. Install the clutch pack into place alternating friction and steel plates. Make sure that all of the steel plates are installed with the same orientation.
If the clutch has multiple clutch plate types, or special components like a judder spring, be sure to install them in the specified order and orientation so the clutch can function as it was intended. Don’t assume these additional parts always sit in the same spot in every clutch pack. Check the service manual to see how these special components are installed as this can vary between models.
Tighten the clutch spring bolts evenly and in a crisscross pattern until the correct torque spec is reached. These bolts can be easily broken by a heavy hand. Assemble the rest of the machine and follow any clutch adjustment procedures for that model.